Device for adjustment of rotor blades which are pivotally mounted on the rotor hub of a wind power plant, with a drive for turning the rotor blades and with a lockout which is connected to the rotor blades.
Wind power plants are plants which are exposed to high stresses. One method of reducing the forces acting on the plant is to use rotor blade adjustment. In addition to the effect of reducing the load, rotor blade adjustment can also be used as a braking system by turning the rotor blades in the direction of the feathered position to shut down the wind power plant and thus the plant loses power and rpm.
Basically the rotor blades, if they are not stopped, have the tendency to turn due to inertial forces and forces of gravity (the center of gravity of the rotor blades is outside their axis of rotation) and external wind forces. The wind forces cause turning of the rotor blades in the direction of the feathered position and the inertial forces cause turning in both directions according to the respective position of the rotor blades during one rotor revolution, the inertial forces mostly predominating.
Turning of the rotor blades beyond the feathered position is conventionally limited by a mechanical stop. If therefore the rotor blades are not stopped, they execute an oscillating rotary motion around their axis of rotation over the course of one rotor revolution, by which the wind power plant cannot be stopped due to wind forces.
In plants according to the prior art which for the most part have three rotor blades, the latter are usually adjusted by a central linear drive in combination with a mechanical rod. Newer systems use mechanical/electrical and mechanical/hydraulic individual blade adjustment. In these systems each rotor blade is adjusted individually and by means of a control unit synchronism of rotor blade adjustment is accomplished. The advantage of individual blade adjustment is that when a drive unit fails the remaining drive units can still be used to turn these rotor blades into the feathered position in order to reliably shut down the plant.
To ensure braking of the plant by rotor blade adjustment even when the power supply fails, in plants of the prior art it is equipped for example with emergency battery power supply or the rotor blades are moved into the working position against a spring force or hydraulic pressure, with which reset of the rotor blades into the feathered position is ensured in any case. Equipping the rotor blade adjustment with an emergency battery power supply is associated with relatively high costs, since the batteries necessary for turning the rotor blades into the feathered position or keeping them in the feathered position until the plant stops must have a not inconsiderable power or capacity.
In the case of adjusting the rotor blades against spring force or hydraulic pressure, correspondingly complex mechanical and hydraulic devices are necessary, and rotor blade adjustment must also be designed for higher loads since the spring force or the force of hydraulics must also be overcome.
U.S. Pat. No. 4,653,982 discloses a wind power plant with a generic adjustment means for rotor blades in which the rotor blades, when reaching a certain maximum rotor rpm, supported by an electromagnet are turned into the feathered position and kept in this position until the rotor rpm again drops below a certain rpm and the rotor blades again turn automatically into the operating position.
U.S. Pat. No. 4,701,104 discloses an adjustment means with a lockout for the rotor blades of a ram-air turbine in which the lockout is kept open by an electromagnet during turbine operation. When the lockout is activated by interruption of the power supply to the electromagnet, the rotor blades are turned into the feathered position by the adjustment means and kept in this position.
U.S. Pat. No. 5,452,988 discloses a gas turbine fan with rotor blade adjustment which has an adjustment means for turning the rotor blades into the operating or feathered position and for stopping the rotor blades in the position which has been set at the time.
The object of the invention is to make available rotor blade adjustment in which turning of the rotor blades into the feathered position when the power supply fails is possible with less technical effort.
The lockout is deactivated in normal operation and when the power supply fails it is activated, by which the rotor blades can only continue to turn into the feathered position and are held there until the plant has come to a standstill.